Methyl mercaptan promoted pyrolysis of olefins



United States Patent O 3 254,136 METHYL MERCAPTAfN PROMOTE!) PYROLYSIS F OLEFENS Kenneth J. Frech, Kent, Ohio, assignor to The Goodyear Tire 8; Rubber Company, Akron, Ohio, a corporation of Ohio N0 Drawing. Filed Feb. 24, 1964, Ser. No. 347,005

14 Claims. (Cl. 260-680) This application is a continuation-in-part of my application, Serial Number 61,818, filed October 11, 1960, and now abandoned.

This invention relates generally to the cracking of olefins. More specifically it relates to a method of improving the efiiciency of cracking olefins by means of a cracking promotor. Most specifically it relates to methods of improving the efficiency of cracking certain specific olefins to form specific diolefins employing a specific cracking promoter.

It is known that most olefins may be thermally decomposed or cracked by subjecting them to relatively high temperatures. By the terms cracking, decocomposing, cracked, decomposed, pyrolysis and pyrolyzing and the like, as employed throughout this application and the claims appended thereto, is meant that the olefin molecule splits into two fragments from the application of heat alone. (This true thermal pyrolysis process is to be distinguished from dehydrogenation processes which require the effect of a surface catalyst as well as high temperatures to remove hydrogen efficiently from molecules to form more unsaturated mole cules.) These fragments themselves become molecules of other lower molecular weight materials which will contain both carbon and hydrogen atoms. This will be explained later in greater detail. Usually the thermal decomposition or cracking of olefins is conducted in a closed zone or reactor at temperatures usually ranging from about 300 C. to about 1000 C. This pyrolysis is usually conducted in the absence of oxygen. Olefins normally are cracked while they are in a gaseous state and may be cracked either relatively pure or as mixtureswith other hydrocarbons, usually in mixture with a saturated hydrocarbon, i.e. a mixed feed stream of pentene and pentane or they may be in mixture with diluents such as nitrogen, steam and the like.

As is indicated, the pyrolysis of olefins usually results in the formation of two lower molecular weight materials each of which contain both carbon and hydrogen atoms. The particular lower molecular weight materials formed when olefins are pyrolyzed depends largely upon the configuration of the olefin subjected to the cracking process. By the term configuration as used throughout this application and claims is meant the position or location of the double bonds and the position or location and type of the side groups, if any, of the olefin in question. To explain this in more detail, an olefin containing 6 carbon atoms with a side methyl group attached to the second carbon atom of the main or straight chain portion and the double bond in the 2 position; such a material is Z-methyl pentene-2, when subjected to cracking, will upon decomposition, produce as the predominant product the di-- olefin, isoprene or 2-methyl butadiene-l,3, and a lower molecular weight paratfin, methane. On the other hand, a 6 carbon olefin having a methyl group attached to the second carbon atoms of the straight chain and the double bond in the 1 position, such a compound is 2-methyl pentene-l, when cracked, will produce as the predominant product two other lower molecular weight olefins, isobutylene and ethylene. Therefore, the configuration of the particular olefin employed usually designates the main or predominant products which result from the cracking of the olefin. These differences in product obtained upon cracking of olefinic isomers are due to the fact that olefins crack at the carbon-to-carbon single bond in the position beta to the double bond, that is, the scission of the olefin occurs at the bond that is in a position beta to the double bond or that the split in the olefin' occurs between the carbon atom next to the carbon which has the double bond attached to it and the carbon adjacent thereto. Thus, to sum up, if olefins are to crack appreciably by the application of heat, they must contain in their make-up a carbon-to-carbon single bond which is in the position beta to the double bond. Therefore, wherever the term cracking of olefins or olefins cracked, decomposed or decomposition or pyrolyzed and the like are employed in this application, is meant olefins which will crack upon the application of heat to form two lower molecular weight olefins or one lower molecular weight diolefin and a saturated hydrocarbon.

Employing the most favorable conditions conducive to cracking of olefins, by application of heat alone, to form lower molecular weight materials, it has been found that olefins decompose at a low rate per pass through the cracking zone. The conditions found conducive to the cracking of olefins are the temperature in the cracking zone, the residence time in the zone and the ratio of the olefin to the diluent, if any, employed. It is usually the practice, to effect an increase in the overall yield of such a process, to separate the unreacted or undecomposed olefin from the products resulting from the decomposition of a portion of the olefin and return or recycle the unreacted olefin to the cracking zone. It has been found, however, regardless of how many recycles are employed the ultimate yield or the ultimate decomposition of the olefin to the desired products at an appreciable yield per pass is not greater than about 45 mol percent of the olefin being decomposed, the remaining 55 mol percent being converted to undesirable or unwanted products as a result of side reactions caused by the high temperature, the long residence time and the recycling steps employed in the cracking process. Thereby, a fairly high percent of these products are, in a sense wasted, in that the starting materials are converted to undesired products.

Therefore, this invention has as its main object a method whereby the overall yield of the desired products produced by cracking an olefin may be increased. Another object is to provide a method whereby the yield per pass of desired products obtained when olefins are cracked may be increased. Another object is to increase the ultimate yield or the ultimate decomposition of olefins to the desired products. Still another object is to provide a method whereby the residence time in the cracking zone of olefins may be decreased. Another object is to provide a method whereby olefins may be cracked at lower cracking temperatures. Another object is to provide a method whereby the formation of undesired products produced by side reactions during the cracking of olefins may be decreased. Another object is to provide a method whereby the size of the equipment necessary to crack a given volume of an olefin is reduced. Another object is to reduce the amount of material required to be recycled. Still another object is to provide a method to promote the cracking of olefins to the desired products. Other objects will become apparent as the description proceeds.

In accordance with the present invention, olefins which contain in their molecules a carbon-to-carbon single bond in a position beta to the double bond, are subjected to temperatures varying from about 400 C. to about 900 C. for periods of time ranging from about 0.001 to about 3 seconds whilesaid olefin is in the presence of a cracking promoter comprising methyl mercaptan, in order to cleave the carbon-to-carbon single bond in the position beta to the double bond of said olefin.

Generally, the cracking of olefins in accordance with the practice of this invention may be carried out in any conventional manner usually employed in the art of cracking olefins. Generally these conditions employed may be widely varied and are not critical. They usually depend upon the particular olefin to be cracked and the particular products which are desired. For instance, the cracking temperature may be varied widely from about 400 C. to about 900 C. However, it is preferred to practice this invention at temperature ranging between 500 and 800 C. and it is more. preferable to employ temperatures ranging from about 600 C to about 750 C. The time that the olefins are in the cracking zone during the practice of this invention may range broadly from about 0.001 to about 3 seconds. However, depending upon the particular olefin cracked and the products desired, this time may vary from about 0.05 to about 1 second and it is most preferred that this time range from about 0.1 to about 0.5 seconds. These times are referred to usually as residence time, that is residence time within the cracking zone and are defined as the time required for 1 molecule of incoming gas, whether it be reactant, diluent or both, to pass through the cracking zone. The cracking zone may be defined as'the zone at which the temperature is elevated to the cracking temperatures as indicated above.

Generally, the olefins which are cracked in accordance with this invention may be in pure form or in mixture with other hydrocarbons. The olefins to be cracked may also be mixed with an inert diluent. It is usually desirable to employ an inert diluent when cracking olefins in accordance with this invention. The term -inert diluent is defined as a material which does not react appreciably or interfere with the olefin to be cracked. Likewise, the diluent does not react with the desired products produced by the cracking at the cracking conditions employed or with the cracking promoter employed in the cracking process. crack or decompose itself at the conditions employed. Examples of diluents suitable for use in this invention are steam, carbon dioxide, hydrogen, nitrogen, the inert gases such as helium, neon and argon or parafiinic hydrocarbons such as methane, ethane, or various other hydrocarbons which themselves will not appreciably crack at the temperatures employed at the carcking conditions of this invention. The ratio of diluent to olefin to be cracked which may be employed in the practice of this invention, if any be employed, may widely vary from about 0.5/1 to about 15 or more mols of diluent per mol of olefin. However, if more than about 15/1 ratio is employed, the improvement gained does not oflFset the cost accrued and the process could become uneconomical. Therefore, itis usually preferred to use a diluent to olefin volume ratio of from about 1/1 about 3/1 or 4/1 in this invention.

The pressure employed in the cracking zone is not critical and may vary from about 1 millimeter of mercury to about 500 pounds per square inch gauge. However,

' it is preferred to employ pressures ranging from about 1 atmosphere to about 100 pounds per square inch gauge in the practice of this invention. Generally, it is usually preferred to employ oxygen-free conditions when practicing this invention.

The amount of methyl mercaptan employed as the olefin pyrolysis promoter in the practice of this invention has been found to vary over a broad range. Of course, sufficient promoter should be employed to obtain an improve- Furthermore, this diluent likewise should not 4 y it has been observed that little, if any, improvement is gained above about mol percent which will warrant the extra expense of more than about 50 mol percent of methyl mercaptan.

As was stated above, this invention is directed to methods of promoting or increasing the efficiency of cracking. olefins which are subject to thermal cracking processes generally. Thus, olefins which, when subjected to the practice of this invention will split at the carbon-tocarbon single bond which is in the position beta to the double bond. It is most desirable to employ the process of this invention with those olefins which has a carbonto-carbon single bond in a position beta to the double bond and which have the proper configuration so that when they decompose they result in products which predominantly form diolefins. t

Representative among the olefins having a carbon-tocarbon single bond which is in a position beta to the double bond which will decompose to form, as a major product, butadiene-1,3 when cracked in the presence of the methyl mercaptan of this invention, are hexene-Z; 3-rnethyl pentene-l; pentene-2;' cyclohexene; 3-methyl butene-l; 2-heptene; 3-methyl hexene-l; S-methyl hexene- 2;.2-octene; S-methyl heptene2; 3,5-dimethyl hexene-l; 3,4,4-trimethy1 pentene-l; 6-methyl heptene-Z; nonene-2; and 3-methyl octenel Representative among the olefins having a carbon-tocarbon single bond which is in a position beta to the double bond which will decompose to form, as a major product, 2-methyl butadiene-1,3 or isoprene when cracked in the presence of the methyl mercaptan of this invention, are 2-methyl pentene-2; 3-methyl pentene-Z; 2-ethyl butene-l; 3,3-dimethyl butene-l; 2,3-dimethyl butene-l; Z-methyl hexene-2; 3-methyl hexene-2; 2-ethyl pentene-l; 2,3-dimethy1 pentene-l; 3,3-dimethyl pentene-l; Z-methyl heptene-Z; 3-methyl heptene-2; 2-ethyl hexene-l; 3,3- dimethyl hexene-l; 2,5-dimethyl hexene-Z; 3,5-dimethyl hexene-2; 4-methyl-2-ethyl pentene-l; 2,3,4-trimethyl pentene-l; 3,3,4-trimethyl pentene-Z; 2-methyl octene-2; 3-methyl octene -2; 3,3-dimethyl heptene-l; 2,5-dimethyl heptene-Z; 2,6-dimethyl heptene-Z; S-methyl-Z-ethyl hexene-l; 3,3,5-trimethyl hexene-l; and 2,5,5-trimethyl hexene-2.

Representative among the olefins having a carbon-tocarbon single bond which is in a position beta to the double bond which will decompose to form, as a major product, Z-ethyl butadiene-1,3 when cracked in the presence of the methyl mercaptan of this invention, are 3- ethyl pentene-2; 2 ethyl pentene-Z; '3 methyl hexene-B; 3-methyl-2-ethyl butene-l; 3 -ethyl hexene-Z; 3-methyl-2- ethyl pentene-l.

Representative among the olefins having a carbon-tocarbon single bond which is in a position beta to the double bond which will decompose to form, as a major product, 2,3-dimethyl butadiene-1,3 when cracked in the presence of the methyl mercaptan of this invention, are 2,3-dimethyl pentene-2; 3-methyl- 2-ethyl butene-l; 2,3,3-trimethyl butene-l; 2-isopropyl pentene-l; 2,3,3-trimethyl pentene-l; and 2,3-dimethyl heptene-2.

Representative among the olefins having a carobn-tocarbon single bond which is in a position beta to the double bond which will decompose to form, as a major product, 3-methyl pentadiene-l,3 when cracked in the presence of the methyl mercaptan of this invention, are 3-methyl hexene-3; 3-ethyl pentene-2; 3-methyl-2-ethyl butene-l; Z-methyl heptene-3; 3,4-dimethyl hexene-Z; 3- methyl-Z-ethyl pentene-l; 3,6-dimethyl heptene-3.

Representative among the olefins having a carbon-tocarbon single bond which is in a position beta to the double bond which will decompose to form, as a major product, Z-methyl pentadiene-1,3 and 4-methyl pentadiene-l,3 when cracked in the presence of the methyl mercaptan of this invention, are hexene-3; Z-ethyl pentene-l; 2,3-dimethyl pentene-l; 2,4-dimethyl pentene-2; 2-methyl heptene-3; 4,4-di-methyl hexene-2; 2-propyl pentene-2; 2-methyl-3-ethy1 pentene-l; 2,6-dimethyl heptene- 3 and 2-propyl hex'ene-l.

Representative among the olefins having a carbon-tocarbon single bond which is in a position beta to the double bond which will decompose to form, as a major product, piperylenes when cracked in the presence of the methyl mercaptan of this invention, are hexene-3; 4- methyl pentene-Z; heptene-3; 4-methyl hexene-Z; octene- 3; 4-met-hyl heptene-2; 6-methyl heptene-3; 3-ethyl hexene-1; 4-methyl-3-ethyl pentene-Z; 4,5-dimethyl heprtene-Z; and 4,5 ,S-trimethyl hexene-2.

The practice of this invention is illustrated by the following experiments which are intended to be representative rather than restrictive of the scope of this invention.

All of the experiments were performed in a cracking assembly consisting of a hairpin coil prepared from inch OD. 316 stainless steel tubing. This cracking coil was immersed in a bed of fluidized heat transfer powder. This heat transfer powder was a microspheroidal aluminasilica material normally employed as a cracking catalyst. This heat transfer powder was heated both by an electrical resistance heater and by cornbusting a natural gas flame directly in the fluidized powder bed. The temperature gradient from the top to the bottom of the bed was never more than about 5 to 6 C. and the gradient from the fluidized bed to the cracking zone was never more than about 5 to 6 C. The temperatures were measured within the fluidized bed by means of conventional'thermocouple techniques. The cracking coil had conventional thermocouple wells and the temperature within the cracking zone was also measured by conventional thermocouple techniques. The procedure employed was to bring the heat transfer powder up to about 500 C. by employing the electrical resistance heaters, at the same time fluidizing the bed by means of air. Then a direct natural gas/ air flame was employed to bring the heat transfer bed up to the desired cracking or operating temperature. The natural gas flame and products of the combustion and additional air was used to fiuidize the powdered bed. The promoter or methyl mercaptan was mixed with the olefin, which was to be cracked, in the desired mol percentage prior to the olefin being passed through the cracking zone. Water and the olefin containingthe promoter, if any, were pumped at the proper rates necessary to produce the desired steam to hydrocarbon ratios and at an overall rate to give the desired residence time of the materials in the cracking zone. The pressure employed was approximately atmospheric. When all variables had been adjusted to give the desired operating conditions, the products of the cracking were collected; if liquid, by means of cooled receivers, and if gas, they were metered at atmospheric pressure and room temperature conditions. The products collected were analyzed for content and yields by conventional analytical methods. Conventional recycle techniques were employed to obtain the ultimate yields and are reported as ultimate reaction efliciencies. The per pass yields are reported as the yield per pass.

The results of each experiment as well as the operaing conditions are reported in the tables below wherein column 1 is the run number; column 2 is the residence time in seconds; column 3 is the temperature employed; column 4 is the promoter employed, if any, and the amount; column 5 is the yield of isoprene reported in mol percent per mol of 3-methyl pentene-2 charged and is the single pass yield and column 6 is the ultimate yield and is reported as the mol percent of isoprene obtained per mol of B-methyl pentene-2 cracked while employing conventional recycle techniques.

In each of these examples products produced are isoprene and methane. All yields and efiiciencies are based on the isoprene produced.

TABLE I.-PYROLYSIS OF 3-METHYL lENTENE-Z Resi- Isoprene Exp. dence Temp, Promoter and Yield] Elli- No. Time, 0. Amount, Mole' Pass, ciency Seconds Percent Mole Percent l 0. 15 667 None 15. 6 61. 2 2* I). 15 661 CHESH 8 Mole 20. 9 72. 1

Percent. 0.15 672 None. 16. 9 61. 7 0. 15 681 None 19. 1 60. 4 0.15 678 (N H928 8 Mole 25. 7 63. 4

Percent. 6 0.15 684 OHgSH 8 Mole 26. 5 77. 0

Percent. 7' 0. 15 702 CH3SH 8 Mole 37. 0 64.1

Percent. 8 0. 15 700 None 26. 2 58. 0

Denotes experiments using CHQSH promoter, the remaining runs are controls and represent thermal pyrolysis of 3methyl pentene-2- As can be observed from the table above, considerable improvement in both yield per pass and efliciencies are obtained in the production of isoprene by the pyrolysis of 3-methyl-2-pentene in the presence of methyl mercaptan. Similar results may be obtained at other operating conditions. Also, similar improvements may be obtained in the cracking of other olefins in accordance with the practice of this invention.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed is:

1. A process to produce isoprene which comprises mixing (1) at least one olefin selected from the group consisting of 2-methyl pentene-2; B-methyl pentene-Z; 2-ethyl butene-l; 3,3-dimethyl butene-l; 2,3-dimethyl butene-l; Z-methyl hexene-Z; S-methyl hexene-Z; and 3,3-dimethyl pentene-l, and (2) at least 0.4 mol percent of methyl mercaptan based on said olefin, subjecting the resulting mixture to temperatures ranging from 500 C. to 800 C. for periods of time from about 0.1 to about 0.5 second and at pressures no greater than about pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming isoprene and recovering said isoprene.

2. A process according to claim 1 in which the olefin is 2-methyl pentene-2.

3. A process according to claim 1 in which the olefin is B-methyl pentene-2.

4. A process to produce 2-ethyl butadiene-1,3 which comprises mixing (1) at least one olefin selected from the group consisting of 3-ethyl pentene-Z; 2-ethyl pentene-Z; and 3-ethyl hexene-2; and (2) at least 0.4 mol percent of methyl mercaptan based on said olefin, subjecting the resulting mixture to temperatures ranging from 500 C. to 800 C. for periods of time from about 0.1 to about 0.5 second and at pressures no greater than about 100 pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming Z-ethyl butadiene-1,3 and recovering said 2-ethyl butadiene-1,3.

5. The method according to claim 4 in which the olefin is 3-ethyl pentene-2.

6. A process to produce butadiene-1,3-which comprises mixing (1) at least one olefin selected from the group consisting of hexene-Z and pentene-2, and. (2) at least 0.4 mol percent of methyl mercaptan based on said olefin, subjecting the resulting mixture to temperatures ranging from 500 C. to 800 C. for periods of time from about 0.1 to about 0.5 second and at pressures no greater than about 100 pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming butadiene-l,3 and recovering said butadiene-1,3.

7. The method according to claim 6 in which the olefin is pentene-Z.

8. A process to produce piperylene which comprises mixing (1) at least one olefin selected from the group consisting of hexene-3; 4-methyl pentene-Z; heptene-3; and 4-methyl hexene-Z, and (2) at least 0.4 mol percent of methyl mercaptan based on said olefin, subjecting the resulting mixture to temperatures ranging from 500 C. to 800 C. for periods of time from about 0.1 to about 0.5 second and at pressures no greater than about 100 pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming piperylene and recovering said piperylene.

9. The method according to claim 8 in which the olefin is hexene-3. Y

10. The method according to claim 8 in which the olefin is 4-methyl pentene-2.-'

11. A process to produce 2,3-dimethyl butadiene-l,3 which comprises mixing (1) at least one olefin selected from the group consisting of 2,3-dimethyl pentene-Z; 3- methyl-Z-ethyl butene-l; 2,3,3-trimethyl butene-l; 2,3,3-

trimethyl pentene-l; and 2,3-dimethyl heptene-2, and (2) at least 0.4 mol percent of methyl mercaptan based on said olefin, subjecting the resulting mixture to temperatures ranging from 500 C. to 800 C. for periods of time from about 0.1 to about 0.5 second and at pressures no greater than about 100 pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming 2,3-dimethyl butadiene-1,3 and recovering said 2,3-dimethyl butadiene-1,3.

12. A process to produce 3-methyl pentadiene-1,3 which comprises mixing (1) at least one olefin selected from the group consisting of B-methyl hexene-3; 3 methyl heptene-3;- and 3,4-dimethyl hexene-2, and (2) at least 0.4 mol percent of methyl mercaptan based on said olefin, subjecting the resulting mixture to temperatures ranging from 500 C. to 800 C. for periods of time from about 0.1 to about 0.5 'second and at pressures no greater than about 100 pounds per square inch, to cleave the carbonto-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming 3-methyl pentadiene-1,3 and recovering said 3-methyl pentadiene- 1,3.

13. A process to produce 2-me'thyl pentadiene-1,3 and 4-methyl pentadiene-1,3 which comprises mixing (1) at least one olefin selected from the group consisting of 2,4- dimethyl pentene-Z; 2-methyl heptene-3; 4,4-dimethyl hexene-2; and 2-propyl pentene-2, and (2) at least 0.4 mol per cent of methyl mercaptan based on said olefin, subjecting the resulting mixture to temperatures ranging from 500 C. to 800 C. for periods of time from about 0.1 to about 0.5 second and at pressures no greater than about 100 pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming 2-methy1 pentadiene- 1,3 and 4-methyl pentadiene-1,3 and recovering said 2; methyl pentadiene-1,3 and 4-methyl pentadiene-1,3.

14. The method of pyrolyzing 2-methy1- pentene-Z which comprises subjecting a mixture of Z-methyl pentene-2 and between about 3 and about 10 mol percent of methyl mercaptan to temperatures ranging from about 600 C. to about 750 C. for periods of time varying from about 0.05 to about 1 second, thereby forming isoprene.

References Cited by the Examiner UNITED STATES PATENTS 2,404,056 7/ 1946 Gorin et al 260-680 2,415,477 2/ 1947 Folkins et a1 260-683 3,104,269 9/1963 Schaffel 260-680 FOREIGN PATENTS 831,249 3/ 1960 Great Britain.

PAUL M. COUGHLAN, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner. 

1. A PROCESS TO PRODUCE ISOPRENE WHICH COMPRISES MIXING (1) AT LEAST ONE OLEFIN SELECTED FROM THE GROUP CONSISTING OF 2-METHYL PENTENE-2; 3-METHYL PENTENE-2; 2-ETHYL BUTENE-1; 3,3-DIMETHYL BUTENE-1; 2,3-DIMETHYL BUTENE-1; 2-METHYL HEXENE-2; 3 METHYL HEXENE-2; AND 3,3-DIMETHYL PENTENE-1, AND (2) AT LEAST 0.4 MOL PERCENT OF METHYL MERCAPTAN BASED ON SAID OLEFIN, SUBJECTING THE RESULTING MIXTURE TO TEMPERATURES RANGING FROM 500*C. TO 800*C. FOR PERIODS OF TIME FROM ABOUT 0.1 TO ABOUT 0.5 SECOND AND AT PRESSURES NO GREATER THAN ABOUT 100 POUNDS PER SQUARE INCH, TO CLEAVE THE CARBON-TO-CARBON SINGLE BOND WHICH IS IN THE POSITION BETA TO THE DOUBLE BOND OF SAID OLEFIN, THEREBY FORMING ISOPRENE AND RECOVERING SAID ISOPRENE. 